This invention relates to the art of metal working machines and, more particularly, to a device for positioning a workpiece and/or holding and stabilizing a portion of a workpiece relative to tooling used to machine the workpiece.
In connection with the machining of bar stock in a lathe, it is of course well known that a length of the bar stock is pushed or pulled through the tubular lathe spindle and chuck to a location spaced outwardly of the chuck at which the outer end of the bar stock is preliminary positioned relative to metal working tools by which the bar stock is to be machined. Such positioning of the bar stock may be relative to tooling on a cross slide displaced transversely of the spindle axis, tooling on a turret rotatable about an axis parallel to the spindle axis, or tooling supported laterally of the spindle axis on the bed or base of the lathe for displacement axially and/or transverse to the spindle axis. As is further well known, such tooling is operable for turning, boring, reaming, end facing, cut-off, and other machining operations. In connection with turrets and cross slides, it is common today to use computer numerically controlled machining techniques (CNC) to achieve, on a continuously repeatable basis, a predetermined sequence of machining operations on the outer end of bar stock rotatably supported on the lathe's chuck. Such computer controlled machining operations are extremely efficient with respect to time and extremely accurate with respect to the duplication of a part being machined.
Heretofore, the positioning of the outer end of bar stock relative to lathe tooling has been achieved by manually pulling the bar stock forwardly of the lathe chuck into abutting engagement with a stop on a cross slide or turret, or pushing the bar stock forwardly of the chuck through the use of a mechanical or hydraulic driving arrangement. As an alternative to such a hard stop, a mechanical or hydraulic bar feeder may advance the bar a predetermined distance to provide the initial position for the machining operations. Most often, end facing of the outer end of the bar stock is the initial machining operation and is necessary to assure accuracy with respect to the subsequent tooling operations and the dimensional accuracy of the part being produced. In addition to the time required for such a facing operation, the time required to initially position the bar stock forwardly of the lathe chuck varies depending on the bar feeder speed or the time to manually position the bar stock to a hard stop. In any event, positioning and end facing are steps which undesirably increase the overall time required to produce a given product. A further problem exists with respect to the fact that mechanical arrangements for gripping and advancing the bar stock relative to the lathe chuck often mar the outer surface of the bar stock and, accordingly, a mark or marks can be left on the outer surface of the final product if the machining operations on the bar stock do not remove a sufficient amount of metal from the outer surface.
Another problem encountered in connection with the machining of bar stock in a lathe occurs during cutting off of an outer end portion of the bar stock or the transverse cutting of the bar stock as the final step in the production of a part. The problem in end cutting occurs as the cut-off tool moves radially inwardly toward the axis of the bar stock and reaches a point at which the remaining metal about the bar stock axis cannot support the weight of the end portion being cut-off. At this point the end portion begins to sag and wobble relative to the bar stock axis which results in pinching of the cut-off tool. Such pinching action is potentially dangerous in that the free end of the workpiece can snap off prior to completion of the cut and become a projectile in the vicinity of the lathe. Furthermore, the pinching action can damage both the end face of the bar stock and the cut-off tool and, at a minimum, causes wearing and thus shortening of the life of the cut-off tool. Damage to the end face of the bar stock requires an end facing operation in connection with the machining of the next product from the bar stock. All of these problems undesirably increase the cost of production per part.